\documentclass{exam-zh}
\examsetup{
  question = {
    show-answer = true,
    show-paren = true
  },
  fillin/type = paren
}

\newcommand{\TTF}{\fillin[$\surd$]}
\newcommand{\TFF}{\fillin[$\times$]}

\begin{document}

\begin{question}
  $1 + 1 = 2$ \TTF
\end{question}

\begin{question}
  $1 + 1 = 3$ \TFF
\end{question}

\end{document}